Prof. Agassiz on Fossil Fishes. 325 



not meet with another difficulty which is opposed to the direct 

 application of these materials to the object in view. The fish 

 of Sheppey belong to the tertiary deposits ; they consequently 

 approach types at present existing. But it is known, and the 

 investigation of the fish of Monte Bolca has sufficiently proved, 

 that the more the families and genera ascend to the older de- 

 posits, the less number of representatives do they possess in 

 the present creation, and these representatives are, moreover, 

 in general met with in distant regions. Thus, of all the large 

 family of the Saroids which formerly peopled the sea, but two 

 representatives remain in the fresh waters of the present cre- 

 ation, while the most numerous families of our epoch, the Si- 

 luri, the Cyprini, the Gadi, and several others, have few or no 

 representatives among fossils. It is, therefore, not among the 

 most common fish of our coasts that Ave must search for the 

 analogues of the fossil tertiary fish. On passing in review the 

 ichthyolites of Monte Bolca, v/e meet with a quantity of fish 

 belonging to families containing few members in our seas, the 

 representatives of which live, for the greater part, only in the 

 Indian Sea, or the Southern Ocean, such as the Squamipenncey 

 the Aulostomata, the Gymnodonts, the Sclerodermata. 



To determine accurately the fish of Monte Bolca, or of the 

 other tertiary deposits, I have been able to call to my aid 

 the materials collected in museums, and especially the skele- 

 tons in the Museum of Paris. The comparisons had princi- 

 pally to be made with the body and the fins, which are toler- 

 ably well-preserved in those fossils, and which are exhibited 

 by the skeleton. To determine the fish of Sheppey, I was 

 obliged to have at my disposal a collection, not less rich, of dis- 

 membered skeletons, detached crania, and of isolated bones ; 

 but it is only possible to form such a collection slowly and at 

 great expense, especially when the person who forms it lives 

 at a distance from the sea, and has at his disposal but a small 

 museum, destined rather to receive typical specimens of genera 

 than series^of specimens of the same species. 



If, notwithstanding these difficulties. I am able to offer at 

 present a tolerably complete sketch of the fossil fish of Shep 

 pey, I owe it to the kindness of English geologists ; in par- 

 ticular of Lord Enniskillen, of Sir Philip Egerton, of Dr 



